The present invention relates generally to the field of composite, heavy-duty, rotary, concrete mixing drums capable of attachment to vehicles and components for use with such drums.
Existing concrete mixing trucks or vehicles that are used to transport concrete from one site to another generally make use of a metal mixing drum. The metal mixing drum is mounted to the vehicle and connected at one end to a drive assembly provided on the vehicle that applies the force needed to rotate the drum. The drive assembly is made up of a gear box that is generally powered by the engine of the vehicle. When the gear box is engaged, the engine provides the power or torque needed to rotate the metal mixing drum around its longitudinal axis. To mix the concrete while the truck is between sites, and to discharge the concrete when the truck reaches the desired location, the metal drum generally includes internal vanes or mixing blades. The vanes are arranged on the inside of the drum in a spiral fashion such that rotation of the drum in one direction mixes the concrete, and rotation of the drum in the opposite direction discharges the concrete through an opening provided on the end of the drum.
Although metal drums have been used for many years, they suffer from a number of disadvantages. First, the construction of metal drums is a relatively labor intensive activity that involves rolling steel sheets into conical portions and cylinders and then coupling the different portions together to form the outer shell of the drum. Once the outer shell of the drum is formed, the mixing blades provided on the inside of the drum generally need to be bolted or welded to the outer shell. Because of the extensive labor required in performing these and other operations, the cost to construct a metal drum can be relatively high.
Second, the internal surfaces of a metal drum tend to wear quickly due to the abrasion on the metal by the concrete, which is increased in the areas where there are abrupt changes in the inner surface of the drum. Thus, the areas in which the mixing blades are welded or bolted to the shell of the drum tend to be areas of increased abrasion that wear rapidly. Moreover, because the concrete tends to slide, rather than roll, along the inside surface of the metal drum, mixing of the concrete tends not to occur along the inside surface of the drum.
Third, metal drums can be relatively heavy due to the weight of the metal used in the construction of the drum. In view of vehicle load limits that place restrictions on the total weight of the vehicle, the heavier the drum, the less concrete can be placed in the drum for transportation to another site. Thus, a truck having a heavier drum may not be able to carry as much payload as a similar truck that has a lighter drum, increasing the long-term operating costs of the truck.
Finally, metal drums tend to absorb and retain heat from the environment and from the exothermic reaction that takes place between the different substances in the concrete. This additional heat retained by the drum tends to decrease the time during which the concrete begins to set. Thus, the distance over which concrete can be moved within mixing trucks that have metal drums is limited.
Attempts have been made to improve the conventional mixing drum. For example, it is known to coat the inside of a metal drum, including the mixing blades, with a resilient wear resistant material. However, while this may improve the wear and mixing characteristics of the traditional metal drum, the coating adds to both the weight of the drum and the costs of manufacturing the drum. Moreover, while reinforced plastic mixing blades have been used in such coated medal drums, the additional step of attaching the mixing blade to the drum requires an additional manufacturing step. It is also know to form the mixing drum from a reinforced plastics material and to then attach the mixing blades to the plastics material. However, like the metal drum, the additional step of attaching the mixing blades adds to the cost of manufacturing the drum.
Due to the differences in the material properties and characteristics of a metal drum and a polymer or composite, drum, some devices and components employed in conventional drums will not work effectively with a composite drum. For example, components such as hatches and drive ring assemblies traditionally used with concrete drums are not compatible with a plastic or composite drum. Moreover, such conventional components tend to be relatively heavy and expensive to manufacture.
Accordingly, it would be advantageous to provide a mixing drum that is cost effective to make and use. It would further be advantageous to provide a mixing drum that is not as labor intensive to produce. It also would be advantageous to provide a mixing drum that is substantially resilient to wear. It would further be advantageous to provide a mixing drum that is capable of withstanding normal loads but is lighter than conventional metal drums. Moreover, it would be advantageous to provide a mixing drum that is not as susceptible to temperature increases as a conventional metal drum. Additionally, it would be advantageous to provide a mixing drum that effectively mixes concrete along the inside surface of the drum. It would also be advantageous to provide components for plastic or composite mixing drums that are suited to the particular properties of the plastic or composite drum and that are lighter and less costly than conventional components for metal mixing drums. It would still further be advantageous to provide a mixing drum that includes any one or more of these or other advantageous features.